Surface temperatures of 56 mammal species were measured using infrared-thermography (IRT) at ambient temperatures from $-$5 to 35 C. Not all species were available at all temperatures. All of the animals' responses were evaluated in terms of effect on heat exchange and thermoregulatory ability. The responses of 21 species were summarized in three-dimensional graphs combining ambient temperature, surface to ambient temperature gradient, and percent of total surface area represented by that gradient. Presented in this manner, the graphs represent heat loss over a wide range of ambient temperatures for each species.The question of whether control of surface temperature is dependent upon body size was evaluated by creating an index of vasomotion (VMI) calculated as: $$\rm VMI = {{SMR \over (SA)(ESAmax)}\over {(T\sb{b}-T\sb{lc})}}(ESA\sb{max}{-}ESA\sb{min}).$$ Standard metabolic rate (SMR) refers to heat output, effective surface area (ESA) refers to the percent of total surface area involved in heat exchange, and the body temperature to lower critical temperature gradient $\rm (T\sb{b}$-$\rm T\sb{lc})$ approximates the range of the thermal neutral zone for each species. Combining these values with the percent change in total surface area involved in heat exchange (ESA$\sb{\rm max}$-ESA$\sb{\rm min})$ yields an index value which reflects the species degree of dependancy upon surface temperature control. By this index, large species are more dependent upon the ability to regulate surface temperature than small species. By considering only those bare or lightly furred surfaces to be involved in heat exchange, measurements of conductance (functional conductance) are essentially the same for all animals.A simplified mathematical model for heat loss in mammals was developed. Instantaneous heat losses calculated from IR images compare favorably to values of oxygen consumption listed in the literature. Using only the species studied, log metabolic rate scales to log body weight by the exponent.808. This reflects a steeper slope than Kleiber's value of.74 because more large species are included.Metabolic rates were estimated by four methods (heat loss model, VMI, Kleiber regression, and the new regression) for species which had not been studied by other investigators. Reasonable prediction were obtained using the three models developed in this study but the VMI model results deviated the least from the new regression. Heat loss model values were assumed to be the best representation of actual instantaneous heat production. Non-invasive techniques such as IRT and modeling can be used effectively to study thermoregulation in rare, expensive, or difficult to handle species.